fix: Characters from unsupported characterset are overlapping (#1958)

## Summary

* **What is the goal of this PR?** fix #1956.

## Additional Context



[NixOS-and-Flakes-Book_ch3_p7_4pct_130044.bmp](https://github.com/user-attachments/files/27648392/NixOS-and-Flakes-Book_ch3_p7_4pct_130044.bmp)

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**< YES >**_

lib/EpdFont/SdCardFont.cpp

@@ -1097,13 +1097,17 @@ int SdCardFont::buildAdvanceTable(const char* utf8Text, uint8_t styleMask) {
 
     uint32_t needCount = 0;
     uint32_t missedThisStyle = 0;
+    const int32_t replacementIdx = findGlobalGlyphIndex(s, REPLACEMENT_GLYPH);
     for (uint32_t i = 0; i < cpCount; i++) {
       const uint32_t cp = codepoints[i];
       if (advanceTableLookup(si, cp, nullptr)) continue;  // already cached
       int32_t idx = findGlobalGlyphIndex(s, cp);
       if (idx < 0) {
-        missedThisStyle++;
-        continue;
+        if (replacementIdx < 0) {
+          missedThisStyle++;
+          continue;
+        }
+        idx = replacementIdx;
       }
       mappings[needCount].codepoint = cp;
       mappings[needCount].glyphIndex = idx;